Vehicle to grid (V2G) technology is expected to be commercialized in the near future. V2G uses the battery in vehicles as energy storage units for power system. It can help balance loads by valley filling and peak shaving. As an energy buffer stage, it will be very helpful for renewable power source, such as wind and solar power, by storing the excess energy during high power output period and providing it back at high load period. To realize the V2G function, a bi-directional on-board charger which can exchange energy between the power grid and a battery is needed. As the on-board charger transfers energy from the alternating current (AC) power system to direct current (DC), a low power factor charger will draw larger current from the power grid than a high power factor one for the same amount of real power consumed. The extra current means energy circulating which brings extra loss as well as the need of larger system capacity. Thus, a power factor correction (PFC) converter is a necessary front stage in medium to high power applications for the on-board charger. The above two reasons require a bi-directional AC-DC converter with PFC function for the on-board charger.
For an electric vehicle charger in SAE AC level 2, the input single phase AC power can be up to 19.2 kW. At this power level, the traditional topology with one inductor at the input stage will be bulky and expensive. However, if a smaller inductor is chosen, the input current harmonics will increase which needs a bigger EMI filter to meet the regulations. If higher switching frequency is adopted to reduce the input current ripple, it means more switching loss and lower efficiency.
For the on-board charger, size and weight is an important factor because the vehicle will always carry the charger. Efficiency is also very important because the energy will be transferred from power source to battery first and then from battery to load again. Every transfer wastes some energy. Low efficiency means huge energy waste. To achieve compact and efficient, there is a need to reduce the passive component size without increasing the switching frequency (the efficiency usually decrease when switching frequency increases).
In this disclosure, a high order input filter for the AC-DC converter is proposed, such that the passive component size can be reduced. The filter integrates both the differential and common mode function and the common mode EMI problem is solved easily. To control a converter with the proposed input filter topology, a model based method with reduced calculation and measurement is also developed, which makes fast and robust performance and low control cost at the same time.
This section provides background information related to the present disclosure which is not necessarily prior art.